First commercially deployed in 1998, network-based wireless location systems (WLS) have been widely deployed in support of location-based services including emergency services location. These network-based wireless location systems collect uplink radio transmissions from a mobile device and then use Time-difference-of-arrival (TDOA), angle of arrival (AoA), and/or signal strength measurement to calculate the location of a mobile device, also known as a Mobile Station (MS), a handset, User Equipment (UE), etc. Network-based systems can also form part of a network-based with mobile-based hybrid location technology.
Network-based WLS normally rely on geographically distributed receivers nominally co-located with the wireless communications network (WCN) base stations to share the receiving antenna, filters, low impedance cabling, and low-noise amplifiers already in use in the base station. The WLS receivers (also called Signal Collection Systems (SCS), Position Determining Equipment (PDE), or Location Measurement Unit (LMU)).
Early work relating to the field of network-based Wireless Location has been described in U.S. Pat. No. 4,728,959; “Direction finding localization system” and U.S. Pat. Nos. 5,327,144; “Cellular Telephone Location System”, and U.S. Pat. No. 5,608,410; “System for Locating a Source of Bursty Transmissions”. These patents are commonly assigned to TruePosition Inc. and are herein incorporated by reference in their entirety.
Code Division Multiple Access (CDMA) is a now common method for transmission of voice and data over radio. TruePosition was a pioneer in location of CDMA mobiles. Location techniques specific to wideband communications system are taught in U.S. Pat. No. 6,047,192; “Robust, Efficient, Localization System”. Location techniques specific to Code Division Multiple Access (CDMA) wireless systems was previously taught in U.S. Pat. No. 7,667,649; “Detection of time of arrival of CDMA signals in a wireless location system”.
Exemplary techniques using downlink receivers in a network-based WLS are taught in TruePosition patent application Ser. No. 11/736,902, filed on Apr. 18, 2007, entitled “Sparsed U-TDOA Wireless Location Networks” and U.S. patent application Ser. No. 11/948,244, filed on Nov. 30, 2007, entitled “Automated Configuration of a Wireless Location System.
The inventive techniques and concepts described herein can be applied to code-division radio communications systems such as CDMAOne (IS-95), CDMA2000 (IS-2000) and the Universal Mobile Telecommunications System (UMTS), the latter of which is also known as W-CDMA. The UMTS model used herein is an exemplary but not exclusive environment in which the present invention may be used.